The present invention relates to methods of manufacturing a multi-layered ceramic substrate having cavities such as IC chip embedding holes.
Multi-layered ceramic substrates (hereafter referred to as MLCs) are employed in a wide range of electronic devices requiring smaller size and higher performance. MLCs are manufactured by laminating multiple green sheets with pre-fabricated via holes and wiring patterns to create a laminated body, and then sintering this laminated body.
MLCs are made thinner by embedding IC chips such as flip chips in cavities created in the substrate. Blind holes and through holes may also be provided in the substrate in accordance with mounting requirements.
In a conventional method for creating cavities in MLCs, a part of a green sheet on which a cavity is to be created is first punched using dies to form the required holes. Accordingly, press dies may need to be re-fabricated every time specifications for cavities are changed, increasing die cost. In addition, for creating cavities extending through more than one green sheet, the hole in each green sheet needs to be aligned before lamination. For this purpose, a different die for aligning needs to be prepared to accurately align the positions of the holes. This raises manufacturing costs as well as adding to the number of manufacturing steps.
Furthermore, even though such jigs are employed, holes cannot be positioned with high accuracy, making the conventional method difficult to apply to recent high-density wiring. In other words, conventional technology is being overtaken by the recent trend towards extremely fine wiring patterns.
On the other hand, to assure dimensional accuracy, since the dimensions of ordinary MLCs change as a result of shrinkage that occurs during sintering, the use of non-shrinkable ceramic substrates is becoming more common. For creating cavities in a non-shrinkable ceramic substrates, a laminated body of green sheets needs to be sandwiched by a material that does not sinter at the sintering temperature of the substrate. The bottoms of cavities also needs to be covered with a material that does not sinter at the sintering temperature of the substrate. However, there is no simple method for accurately applying a non-sintering material at the bottom of a cavity, making the creation of cavities in non-shrinkable ceramic substrate problematic.
The present invention aims to provide a method of manufacturing MLCs which does not require expensive dies or hole aligning processes.
In the present invention, a sintering preventive process is applied to a part of a green sheet which will become the bottom of a cavity in a MLC to prevent sintering of adjacent green sheets. Then, the inner wall of the cavity is cut all the way to the bottom of the cavity, and the inside sintered portion of the cavity is removed. This facilitates the formation of the cavity. Accordingly, the present invention enables rapid creation of a cavity even where a cavity extends through several green sheets, without using expensive dies.
More specifically, the method for manufacturing MLCs of the present invention comprises the following steps.
i) A plurality of green sheets having pre-fabricated via holes and wiring patterns are laminated to create a laminated body;
ii) The laminated body is sintered to create a multi-layered sintered body wherein the laminated body contains a green sheet in which a cavity is formed, and a sintering preventive materials is applied between adjacent green sheets in an area which will become the bottom of the cavity; and
iii) The inner wall of a cavity is cut all the way to the bottom of the cavity, and then a sintered portion is removed leaving the cavity.